Cancer markers are substances that can be found in the body (usually in the blood or urine) when cancer is present. They can be products of the cancer cells themselves, or of the body in response to cancer or other conditions. For several reasons, cancer markers themselves are usually not enough to diagnose (or rule out) a specific type of cancer. Most cancer markers can be produced by normal cells as well as by cancer cells, even if in smaller amounts. Sometimes, non-cancerous diseases can also cause levels of certain cancer markers to be higher than normal. Further, not every person with cancer may have higher levels of a cancer marker. For these reasons, only a small amount of cancer markers are commonly used by most doctors. When a doctor does look at the level of a certain cancer marker, he or she will typically consider it along with the results of the patient's history and physical exam, and other lab tests or imaging tests.
Screening refers to looking for cancer in individuals who have no symptoms of the disease, while early detection is finding cancer at an early stage of the disease, when it is less likely to have spread (and is more likely to be treated effectively). Although cancer markers were originally investigated and developed to test for cancer in people without symptoms, very few markers have been shown to be helpful in this way.
Ovarian cancer has the highest mortality among gynecological cancers. The lack of early symptoms and the absence of a reliable screening test to detect ovarian cancer result in over 70% of women being diagnosed after the disease has spread beyond the ovary so that the prognosis is poor with approximately 12,000 deaths due to ovarian cancer annually (5-year survival is no better than 37%). Currently, physical pelvic examination by a physician, ultrasound or measuring blood levels for CA125 are the only standard methods available for detection of ovarian cancer. However, none of these methods provides a reliably consistent and accurate method to detect ovarian cancer. For example, while over 80% of women with ovarian cancer will have elevated blood levels of CA125, blood levels of CA125 are only about 50% accurate for detecting early stage disease. The development of an alternate and new test to reliably and accurately detect all ovarian cancers is imperative. Thus, what is needed is a technology that overcomes the current lack of a reliable, accurate, safe and cost-effective test for ovarian cancer. Furthermore, what is needed is a technology that accurately detects all ovarian cancers, many of which now go undetected, as well as monitor disease burden throughout the course of ovarian cancer.
An accurate, safe, simple, and reliable test to diagnosis ovarian cancer would benefit all women, in the United States and worldwide, including medically underserved geographical areas and especially women at high risk for developing ovarian cancer. Given that approximately 25,000 women are diagnosed with ovarian cancer annually in the U.S., a biomarker of ovarian cancer that is detectable in both early and late stages of disease would not only confirm the diagnosis of ovarian cancer, but could also potentially detect thousands of previously undiagnosed ovarian cancers. This is especially important for detection of ovarian cancer in early stages where the disease is confined to the ovary, but currently accounts for less than 10% of diagnosed ovarian cancers. In these situations, surgical debulking of the diseased ovary increases patient survival to over 90% and would be expected to reduce medical costs. The ability to accurately detect and monitor ovarian cancer in each patient through the course of her disease, would not only serve for initial ovarian cancer diagnosis, but would also indicate therapeutic efficacy and/or recurrent disease. The development of a commercially available, FDA-approved ELISA-based test, for example, could become the gold standard for clinical diagnosis of ovarian cancer.
While apoptosis is an essential biological process for normal development and maintenance of tissue homeostasis, it is also involved in a number of pathologic conditions including tissue injury, degenerative diseases, immunological diseases and cancer (Lowe, S. W. and Lin, A. W. Carcinogenesis, 2000, 21:485-495). Whether activated by membrane bound death receptors (Ashkenazi, A. et al. J. Clin. Invest., 1999, 104:155-162; Walczak, H. Krammer, P. H. Exp. Cell Res, 2000, 256:58-66) or by stress-induced mitochondrial perturbation with subsequent cytochrome c release (Loeffler, M. and Kroemer, G. Exp. Cell Res., 2000, 256:19-26; Wernig, F. and Xu, Q. Prog. Biophys. Mol. Biol., 2002, 78:105-137; Takano, T. et al. Antiox. Redox. Signal, 2002, 4:533-541), activation of downstream caspases leads to stepwise cellular destruction by disrupting the cytoskeleton, shutting down DNA replication and repair, degrading chromosomal DNA, and, finally, disintegrating the cell into apoptotic bodies (Nagata, S. Exp. Cell Res., 2000, 256:12-18). The key regulators of apoptosis include members of the bcl-2 protein family (Farrow, S. N. and Brown, R. Curr. Opin. Gen. Dev., 1996, 6:45-49).
The bcl-2 protein family consists of both pro- and anti-apoptotic protein family members that act at different levels of the apoptotic cascade to regulate apoptosis. The bcl-2 family members contain at least one Bcl-2-homology (BH) domain (Farrow, S. N. and Brown, R. Curr. Opin. Gen. Dev., 1996, 6:45-49). Though all bcl-2 family members demonstrate membrane channel forming activity, Bcl-2 (the archetypal bcl-2 family member) channels are cation (Ca++) selective and, owing to its exclusive ER and mitochondrial membrane localization (Thomenius, M. J. and Distelhorst, C. W. J. Cell Sci., 2003, 116:4493-4499), the anti-apoptotic function of Bcl-2 is at least partly mediated by its ability to prevent calcium release from the ER and subsequent mitochondrial membrane perturbation and cytochrome c release. Since Bcl-2 is overexpressed in many tumor types including ovarian cancer (Sharma, H. et al. Head Neck, 2004, 26:733-740; Hanaoka, T. et al. Intl. J. Clin. Oncol., 2002, 7:152-158; Trisciuoglio, D. et al. J. Cell Physiol., 2005, 205:414-421; Khalifeh, I. et al. Int. J. Gynecol. Pathol., 2004, 23:162-169; O'Neill, C. J. et al. Am. J. Surg. Pathol.; 2005, 29:1034-1041), it contributes to chemoresistance by stabilizing the mitochondrial membrane against apoptotic insults. Currently, preclinical studies focus on the development of agents to inhibit Bcl-2, including antisense oligonucleotides such as G3,139 (Ackermann, E. J. et al. J. Biol. Chem., 1999, 274:11245-11252), and small molecular inhibitors of Bcl-2 (Lickliter, J. D. et al. Leukemia, 2003, 17:2074-2080). Though such studies target Bcl-2 for therapeutic intervention, quantification of urinary Bcl-2 has not previously been reported in the literature.
It would be advantageous to have available assays that provide safe, sensitive, specific, and economical methods for the detection of cancers such as ovarian cancer, which would benefit society worldwide.